The present invention relates to hologram synthesis from two-dimensional (2-D) transparencies and is particularly concerned with a new and improved method and hologram for reconstructing three-dimensional (3-D) objects from the multiple views of the objects recorded separately.
Large outdoor scenes such as monuments, buildings, ships etc. cannot be directly recorded on usual holograms. However, there are methods of 3-D hologram synthesis from 2-D photographic transparencies that make multiplex holograms from which 3-D outdoor objects can be reconstructed.
In priciple there are two basic techniques for constructing the multiplex holograms. Individual basic holograms are multiplexed either on a whole holographic plate overlapping each other or on adjacent small areas contiguous over a holographic plate. These areas are mostly vertical stripes, but theoretically small rectangles arranged in a 2-D lattice may be used instead of the stripes. Methods that are something between the two above-mentioned techniques have been also applied in practice.
The method where the individual basic holograms overlap each other suffers from the serious fall-off of the diffraction efficiency with the increasing number of multiplexed holograms and is essentially useless from a practical standpoint. Attempts to alleviate this drawback, for instance by hologram copying or by using litium niobate for hologram recording, are not satisfactory enough.
The stripe recording technique does not suffer from the above mentioned drawback. However, there are other shortcomings in this technique. First, the application of the stripe holograms brings the loss of one of two parallaxes. This means that a holographic stereogram constructed by this technique can reconstruct an image with only one parallax. It is the horizontal parallax which is mostly recorded. Second, the plane of such a hologram is the plane of adjacent pupils for the direction perpendicular to the stripes. For viewing such a multiplex hologram the eye pupil ought to be placed as close to the hologram as possible so as not to reduce the impression from the stereoscopic reconstruction. When the eye pupil is not close enough to this type of multiplex hologram, the different parts of a reconstructed object are viewed through different individual basic holograms (stripes) for a static position of the eye pupil and this fact causes the mentioned reduction of the impression from the stereoscopic reconstruction. The eye pupil at the plane of the hologram would have represented the optimum case for viewing the reconstructed synthetic image. Of course, this can never be achieved because of the impossibility of placing the eye onto a large mechanical plate. Moreover, it is obvious that it would not be suitable to view the hologram from some excessive distance. However, there is another reason which constrains one to view this type of hologram from a long distance. The other reason is connected with white-light reconstruction and the rainbow holographic technique.
The white-light reconstruction of a hologram (which is a necessary condition for certain commercial purposes) can be realized by using a reflection hologram or by using some version of rainbow holography. The rainbow method unconditionally requires placing the pupil of an imagery for the direction perpendicular to the "holographic grating" far enough from the holographic plate. Consequently, we must also place the eye pupil viewing the reconstruction far enough from the hologram. This means that from the point of view of the successful rainbow reconstruction, the requirement of placing an eye far from the hologram is contrary to the requirement for a fully successful steroscopic reconstruction which requires placing the eye as close to the hologram as possible. In practice, the priority is given to the former requirement so that the steroscopic impression is partially lost. Of course it is impossible to view a reflection hologram from a vicinity without obstructing the reconstruction beam, so that the version replacing the rainbow method by a reflection hologram would not bring an improvement.
To summarize, up to this time there has not been a method for making synthetic holograms from 2-D transparencies which would quite successfully reconstruct 3-D objects either in white-light or with help of only a laser.
The present invention is directed to a new synthetic hologram and the method of its creation. This hologram is referred to as the synthetic field hologram and for shortness designated by the letters SFH. With help of the disclosed method and SFH it will be possible to record and reconstruct generally in white-light any 3-D object without loss of any parallax. This means, that with this invention it will be also possible to make 2-D holographic maps providing the 3-D images of recorded territories. The reconstructed synthetic image of an object made with a required magnification and with or without changed parallaxes can be one-color or full-color. The most suitable distance for viewing the SFH can be a priori selected. The diffraction efficiency of the SFH is not dependent on the number of basic holograms, i.e. on the number of the recorded views of the objects, and the reconstructed image can be viewing without vignetting and with the maximum possible impression from the volume reconstruction. It is also possible for a series of SFH's to be readily made.
The aforementioned features, advantages and benefits of the invention, along with additional ones, will be seen in the ensuing description of one possible embodiment and claims which should be considered in conjunction with the accompanying drawing.
The drawing promotes easier understanding of the embodiment of the invention showing only one of many possible arrangements that can be considered for the practicing the invention.